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100 mL of a buffer solution contains 0.1...

100 mL of a buffer solution contains 0.1 M each of weak acid HA and salt NaA. How many gram of NaOH should be added to the buffer so that it pH will be 6? `(K_(a) of DeltaA= 10^(-5))`

A

`0.328`

B

`0.458`

C

`4.19`

D

`1.32`

Text Solution

Verified by Experts

The correct Answer is:
A
For acidic buffer, `pH = pK _(4) + log "" (0.1)/(0.1), pH = pK _(a) = - log (10 ^(-5)) = 5.`
Rule, ABA (In acidic buffer (A), on addition of `S _(B) (B),` the concentratio of `W _(A) (A)` decreases and that of salt in creases. Let x M of Na OH is added,
`pH _(n ew) = 5 + log ((0.1 + x)/( 0.1 - x )) , 6-5 = log ((0.1 + x )/( 0. 1 - x )) ,((0.1 + x )/( 0. 1 - x)) =` Antilog `(1) = 10`
Solve for x,
`x = 0.082 M = (0.082 )/(1000) xx 100 0.0082 mol ( 100 mL ) ^(-1) = 0.0082 xx 40 g (100 mL) ^(-1) = 0.328 g`
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